Because machinery and vehicles present during their life cycle, meaning from the manufacturing to the disassembly, a possible danger for mankind, machinery or vehicle, respectively, and the environment, these hazards are ascertained during the design phase and attempts are made through appropriate actions to reduce the same. Hereby, the overall safety of a machine or vehicle, respectively, describes the condition which does not present any unjustifiable risks for mankind or is considered as no danger. The term functional safety describes, however, a part of the overall safety of a system which is dependent of the concrete function of the safety related systems and external devices for risk reduction.
The parts of machinery or vehicle controls which are responsible for safety tasks are marked by international norms as safety related parts or controls. These parts can comprise of hardware or software and can be a separate or integral part of the machine control or vehicle control, respectively. Safety related control parts each incorporate the entire reaction chain of a safety function, comprising of an input-level, such as a sensor, the logic, meaning a safe signal processing, and the output-level, which is for instance realized through an actuator.
It is the common goal to design these control parts in such a way that the safety of the control function, as well as the behavior of the control in case of a malfunction, corresponds to the level of risk reduction which was determined in a risk assessment.
To monitor the function of bidirectional actuated hydraulic shift elements, such as clutch pistons or control pistons, the state of the art uses in known transmission devices constructively sophisticated distance sensor configurations or pressure sensor configurations, respectively. Hereby, the distance sensors which are used are either very expensive analog sensors or at least end position switches are implemented. The application of such distance sensors or end position switches increases the constructive complexity of a transmission device, because the position of a clutch piston in a transmission device, for instance, can only be determined directly at its location, meaning directly in the area of the respective transmission part.
If the function of rotating transmission parts, which are in operation in a transmission device, need to be monitored, a device to determine the operating condition has to be at least partially designed with a telemetric data measuring device, which would be disadvantageous in a series production due to high cost.